FreeBSD Manual Pages

IPFW(8) FreeBSD System Manager's Manual IPFW(8)
NAMEipfw -- User interface for firewall, traffic shaper, packet scheduler,
in-kernel NAT.
SYNOPSISFIREWALLCONFIGURATIONipfw [-cq] addruleipfw [-acdefnNStT] [setN] {list | show} [rule | first-last...]
ipfw [-f | -q] [setN] flushipfw [-q] [setN] {delete | zero | resetlog} [number...]
ipfwset [disablenumber...] [enablenumber...]
ipfwsetmove [rule] numbertonumberipfwsetswapnumbernumberipfwsetshowSYSCTLSHORTCUTSipfwenable
{firewall | altq | one_pass | debug | verbose | dyn_keepalive}
ipfwdisable
{firewall | altq | one_pass | debug | verbose | dyn_keepalive}
LOOKUPTABLESipfw [setN] tablenamecreatecreate-optionsipfw [setN] table {name | all} destroyipfw [setN] tablenamemodifymodify-optionsipfw [setN] tablenameswapnameipfw [setN] tablenameaddtable-key [value]
ipfw [setN] tablenameadd [table-keyvalue...]
ipfw [setN] tablenameatomicadd [table-keyvalue...]
ipfw [setN] tablenamedelete [table-key...]
ipfw [setN] tablenamelookupaddripfw [setN] tablenamelockipfw [setN] tablenameunlockipfw [setN] table {name | all} listipfw [setN] table {name | all} infoipfw [setN] table {name | all} detailipfw [setN] table {name | all} flushDUMMYNETCONFIGURATION(TRAFFICSHAPERANDPACKETSCHEDULER)ipfw {pipe | queue | sched} numberconfigconfig-optionsipfw [-s [field]] {pipe | queue | sched} {delete | list | show}
[number...]
IN-KERNELNATipfw [-q] natnumberconfigconfig-optionsipfw [-cfnNqS] [-ppreproc [preproc-flags]] pathnameSTATEFULIPv6/IPv4NETWORKADDRESSANDPROTOCOLTRANSLATIONipfw [setN] nat64lsnnamecreatecreate-optionsipfw [setN] nat64lsnnameconfigconfig-optionsipfw [setN] nat64lsn {name | all} {list | show} [states]
ipfw [setN] nat64lsn {name | all} destroyipfw [setN] nat64lsnnamestats [reset]
STATELESSIPv6/IPv4NETWORKADDRESSANDPROTOCOLTRANSLATIONipfw [setN] nat64stlnamecreatecreate-optionsipfw [setN] nat64stlnameconfigconfig-optionsipfw [setN] nat64stl {name | all} {list | show}
ipfw [setN] nat64stl {name | all} destroyipfw [setN] nat64stlnamestats [reset]
IPv6-to-IPv6NETWORKPREFIXTRANSLATIONipfw [setN] nptv6namecreatecreate-optionsipfw [setN] nptv6 {name | all} {list | show}
ipfw [setN] nptv6 {name | all} destroyipfw [setN] nptv6namestats [reset]
INTERNALDIAGNOSTICSipfwinternaliflistipfwinternaltalistipfwinternalvlistDESCRIPTION
The ipfw utility is the user interface for controlling the ipfw(4) fire-
wall, the dummynet(4) traffic shaper/packet scheduler, and the in-kernel
NAT services.
A firewall configuration, or ruleset, is made of a list of rules numbered
from 1 to 65535. Packets are passed to the firewall from a number of
different places in the protocol stack (depending on the source and des-
tination of the packet, it is possible for the firewall to be invoked
multiple times on the same packet). The packet passed to the firewall is
compared against each of the rules in the ruleset, in rule-number order
(multiple rules with the same number are permitted, in which case they
are processed in order of insertion). When a match is found, the action
corresponding to the matching rule is performed.
Depending on the action and certain system settings, packets can be rein-
jected into the firewall at some rule after the matching one for further
processing.
A ruleset always includes a default rule (numbered 65535) which cannot be
modified or deleted, and matches all packets. The action associated with
the default rule can be either deny or allow depending on how the kernel
is configured.
If the ruleset includes one or more rules with the keep-state or limit
option, the firewall will have a stateful behaviour, i.e., upon a match
it will create dynamicrules, i.e., rules that match packets with the
same 5-tuple (protocol, source and destination addresses and ports) as
the packet which caused their creation. Dynamic rules, which have a lim-
ited lifetime, are checked at the first occurrence of a check-state,
keep-state or limit rule, and are typically used to open the firewall on-
demand to legitimate traffic only. See the STATEFULFIREWALL and
EXAMPLES Sections below for more information on the stateful behaviour of
ipfw.
All rules (including dynamic ones) have a few associated counters: a
packet count, a byte count, a log count and a timestamp indicating the
time of the last match. Counters can be displayed or reset with ipfw
commands.
Each rule belongs to one of 32 different sets , and there are ipfw com-
mands to atomically manipulate sets, such as enable, disable, swap sets,
move all rules in a set to another one, delete all rules in a set. These
can be useful to install temporary configurations, or to test them. See
Section SETSOFRULES for more information on sets.
Rules can be added with the add command; deleted individually or in
groups with the delete command, and globally (except those in set 31)
with the flush command; displayed, optionally with the content of the
counters, using the show and list commands. Finally, counters can be
reset with the zero and resetlog commands.
COMMANDOPTIONS
The following general options are available when invoking ipfw:
-a Show counter values when listing rules. The show command implies
this option.
-b Only show the action and the comment, not the body of a rule.
Implies -c.
-c When entering or showing rules, print them in compact form, i.e.,
omitting the "ip from any to any" string when this does not carry
any additional information.
-d When listing, show dynamic rules in addition to static ones.
-e When listing and -d is specified, also show expired dynamic
rules.
-f Do not ask for confirmation for commands that can cause problems
if misused, i.e., flush. If there is no tty associated with the
process, this is implied.
-i When listing a table (see the LOOKUPTABLES section below for
more information on lookup tables), format values as IP
addresses. By default, values are shown as integers.
-n Only check syntax of the command strings, without actually pass-
ing them to the kernel.
-N Try to resolve addresses and service names in output.
-q Be quiet when executing the add, nat, zero, resetlog or flush
commands; (implies -f). This is useful when updating rulesets by
executing multiple ipfw commands in a script (e.g.,
`sh /etc/rc.firewall'), or by processing a file with many ipfw
rules across a remote login session. It also stops a table add
or delete from failing if the entry already exists or is not
present.
The reason why this option may be important is that for some of
these actions, ipfw may print a message; if the action results in
blocking the traffic to the remote client, the remote login ses-
sion will be closed and the rest of the ruleset will not be pro-
cessed. Access to the console would then be required to recover.
-S When listing rules, show the set each rule belongs to. If this
flag is not specified, disabled rules will not be listed.
-s [field]
When listing pipes, sort according to one of the four counters
(total or current packets or bytes).
-t When listing, show last match timestamp converted with ctime().
-T When listing, show last match timestamp as seconds from the
epoch. This form can be more convenient for postprocessing by
scripts.
LISTOFRULESANDPREPROCESSING
To ease configuration, rules can be put into a file which is processed
using ipfw as shown in the last synopsis line. An absolute pathname must
be used. The file will be read line by line and applied as arguments to
the ipfw utility.
Optionally, a preprocessor can be specified using -ppreproc where
pathname is to be piped through. Useful preprocessors include cpp(1) and
m4(1). If preproc does not start with a slash (`/') as its first charac-
ter, the usual PATH name search is performed. Care should be taken with
this in environments where not all file systems are mounted (yet) by the
time ipfw is being run (e.g. when they are mounted over NFS). Once -p
has been specified, any additional arguments are passed on to the pre-
processor for interpretation. This allows for flexible configuration
files (like conditionalizing them on the local hostname) and the use of
macros to centralize frequently required arguments like IP addresses.
TRAFFICSHAPERCONFIGURATION
The ipfwpipe, queue and sched commands are used to configure the traffic
shaper and packet scheduler. See the TRAFFICSHAPER(DUMMYNET)CONFIGURATION Section below for details.
If the world and the kernel get out of sync the ipfw ABI may break, pre-
venting you from being able to add any rules. This can adversely affect
the booting process. You can use ipfwdisablefirewall to temporarily
disable the firewall to regain access to the network, allowing you to fix
the problem.
PACKET FLOW
A packet is checked against the active ruleset in multiple places in the
protocol stack, under control of several sysctl variables. These places
and variables are shown below, and it is important to have this picture
in mind in order to design a correct ruleset.
^ to upper layers V
| |
+----------->-----------+
^ V
[ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1
| |
^ V
[ether_demux] [ether_output_frame] net.link.ether.ipfw=1
| |
+-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1
^ V
| to devices |
The number of times the same packet goes through the firewall can vary
between 0 and 4 depending on packet source and destination, and system
configuration.
Note that as packets flow through the stack, headers can be stripped or
added to it, and so they may or may not be available for inspection.
E.g., incoming packets will include the MAC header when ipfw is invoked
from ether_demux(), but the same packets will have the MAC header
stripped off when ipfw is invoked from ip_input() or ip6_input().
Also note that each packet is always checked against the complete rule-
set, irrespective of the place where the check occurs, or the source of
the packet. If a rule contains some match patterns or actions which are
not valid for the place of invocation (e.g. trying to match a MAC header
within ip_input or ip6_input), the match pattern will not match, but a
not operator in front of such patterns will cause the pattern to always
match on those packets. It is thus the responsibility of the programmer,
if necessary, to write a suitable ruleset to differentiate among the pos-
sible places. skipto rules can be useful here, as an example:
# packets from ether_demux or bdg_forward
ipfw add 10 skipto 1000 all from any to any layer2 in
# packets from ip_input
ipfw add 10 skipto 2000 all from any to any not layer2 in
# packets from ip_output
ipfw add 10 skipto 3000 all from any to any not layer2 out
# packets from ether_output_frame
ipfw add 10 skipto 4000 all from any to any layer2 out
(yes, at the moment there is no way to differentiate between ether_demux
and bdg_forward).
SYNTAX
In general, each keyword or argument must be provided as a separate com-
mand line argument, with no leading or trailing spaces. Keywords are
case-sensitive, whereas arguments may or may not be case-sensitive
depending on their nature (e.g. uid's are, hostnames are not).
Some arguments (e.g., port or address lists) are comma-separated lists of
values. In this case, spaces after commas ',' are allowed to make the
line more readable. You can also put the entire command (including
flags) into a single argument. E.g., the following forms are equivalent:
ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8
ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8
ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8"
RULE FORMAT
The format of firewall rules is the following:
[rule_number] [setset_number] [probmatch_probability] action
[log [logamountnumber]] [altqqueue] [{tag | untag} number] body
where the body of the rule specifies which information is used for fil-
tering packets, among the following:
Layer-2 header fields When available
IPv4 and IPv6 Protocol SCTP, TCP, UDP, ICMP, etc.
Source and dest. addresses and ports
Direction See Section PACKETFLOW
Transmit and receive interface By name or address
Misc. IP header fields Version, type of service, data-
gram length, identification,
fragment flag (non-zero IP off-
set), Time To Live
IP options
IPv6 Extension headers Fragmentation, Hop-by-Hop
options, Routing Headers, Source
routing rthdr0, Mobile IPv6
rthdr2, IPSec options.
IPv6 Flow-ID
Misc. TCP header fields TCP flags (SYN, FIN, ACK, RST,
etc.), sequence number, acknowl-
edgment number, window
TCP options
ICMP types for ICMP packets
ICMP6 types for ICMP6 packets
User/group ID When the packet can be associ-
ated with a local socket.
Divert status Whether a packet came from a
divert socket (e.g., natd(8)).
Fib annotation state Whether a packet has been tagged
for using a specific FIB (rout-
ing table) in future forwarding
decisions.
Note that some of the above information, e.g. source MAC or IP addresses
and TCP/UDP ports, can be easily spoofed, so filtering on those fields
alone might not guarantee the desired results.
rule_number
Each rule is associated with a rule_number in the range 1..65535,
with the latter reserved for the default rule. Rules are checked
sequentially by rule number. Multiple rules can have the same
number, in which case they are checked (and listed) according to
the order in which they have been added. If a rule is entered
without specifying a number, the kernel will assign one in such a
way that the rule becomes the last one before the default rule.
Automatic rule numbers are assigned by incrementing the last non-
default rule number by the value of the sysctl variable
net.inet.ip.fw.autoinc_step which defaults to 100. If this is
not possible (e.g. because we would go beyond the maximum allowed
rule number), the number of the last non-default value is used
instead.
setset_number
Each rule is associated with a set_number in the range 0..31.
Sets can be individually disabled and enabled, so this parameter
is of fundamental importance for atomic ruleset manipulation. It
can be also used to simplify deletion of groups of rules. If a
rule is entered without specifying a set number, set 0 will be
used.
Set 31 is special in that it cannot be disabled, and rules in set
31 are not deleted by the ipfwflush command (but you can delete
them with the ipfwdeleteset31 command). Set 31 is also used
for the default rule.
probmatch_probability
A match is only declared with the specified probability (floating
point number between 0 and 1). This can be useful for a number
of applications such as random packet drop or (in conjunction
with dummynet) to simulate the effect of multiple paths leading
to out-of-order packet delivery.
Note: this condition is checked before any other condition,
including ones such as keep-state or check-state which might have
side effects.
log [logamountnumber]
Packets matching a rule with the log keyword will be made avail-
able for logging in two ways: if the sysctl variable
net.inet.ip.fw.verbose is set to 0 (default), one can use bpf(4)
attached to the ipfw0 pseudo interface. This pseudo interface
can be created after a boot manually by using the following com-
mand:
# ifconfig ipfw0 create
Or, automatically at boot time by adding the following line to
the rc.conf(5) file:
firewall_logif="YES"
There is no overhead if no bpf(4) is attached to the pseudo
interface.
If net.inet.ip.fw.verbose is set to 1, packets will be logged to
syslogd(8) with a LOG_SECURITY facility up to a maximum of
logamount packets. If no logamount is specified, the limit is
taken from the sysctl variable net.inet.ip.fw.verbose_limit. In
both cases, a value of 0 means unlimited logging.
Once the limit is reached, logging can be re-enabled by clearing
the logging counter or the packet counter for that entry, see the
resetlog command.
Note: logging is done after all other packet matching conditions
have been successfully verified, and before performing the final
action (accept, deny, etc.) on the packet.
tagnumber
When a packet matches a rule with the tag keyword, the numeric
tag for the given number in the range 1..65534 will be attached
to the packet. The tag acts as an internal marker (it is not
sent out over the wire) that can be used to identify these pack-
ets later on. This can be used, for example, to provide trust
between interfaces and to start doing policy-based filtering. A
packet can have multiple tags at the same time. Tags are
"sticky", meaning once a tag is applied to a packet by a matching
rule it exists until explicit removal. Tags are kept with the
packet everywhere within the kernel, but are lost when packet
leaves the kernel, for example, on transmitting packet out to the
network or sending packet to a divert(4) socket.
To check for previously applied tags, use the tagged rule option.
To delete previously applied tag, use the untag keyword.
Note: since tags are kept with the packet everywhere in ker-
nelspace, they can be set and unset anywhere in the kernel net-
work subsystem (using the mbuf_tags(9) facility), not only by
means of the ipfw(4)tag and untag keywords. For example, there
can be a specialized netgraph(4) node doing traffic analyzing and
tagging for later inspecting in firewall.
untagnumber
When a packet matches a rule with the untag keyword, the tag with
the number number is searched among the tags attached to this
packet and, if found, removed from it. Other tags bound to
packet, if present, are left untouched.
altqqueue
When a packet matches a rule with the altq keyword, the ALTQ
identifier for the given queue (see altq(4)) will be attached.
Note that this ALTQ tag is only meaningful for packets going
"out" of IPFW, and not being rejected or going to divert sockets.
Note that if there is insufficient memory at the time the packet
is processed, it will not be tagged, so it is wise to make your
ALTQ "default" queue policy account for this. If multiple altq
rules match a single packet, only the first one adds the ALTQ
classification tag. In doing so, traffic may be shaped by using
countaltqqueue rules for classification early in the ruleset,
then later applying the filtering decision. For example,
check-state and keep-state rules may come later and provide the
actual filtering decisions in addition to the fallback ALTQ tag.
You must run pfctl(8) to set up the queues before IPFW will be
able to look them up by name, and if the ALTQ disciplines are
rearranged, the rules in containing the queue identifiers in the
kernel will likely have gone stale and need to be reloaded.
Stale queue identifiers will probably result in misclassifica-
tion.
All system ALTQ processing can be turned on or off via ipfwenablealtq and ipfwdisablealtq. The usage of
net.inet.ip.fw.one_pass is irrelevant to ALTQ traffic shaping, as
the actual rule action is followed always after adding an ALTQ
tag.
RULEACTIONS
A rule can be associated with one of the following actions, which will be
executed when the packet matches the body of the rule.
allow | accept | pass | permit
Allow packets that match rule. The search terminates.
check-state [:flowname | :any]
Checks the packet against the dynamic ruleset. If a match is
found, execute the action associated with the rule which gener-
ated this dynamic rule, otherwise move to the next rule.
Check-state rules do not have a body. If no check-state rule is
found, the dynamic ruleset is checked at the first keep-state or
limit rule. The :flowname is symbolic name assigned to dynamic
rule by keep-state opcode. The special flowname :any can be used
to ignore states flowname when matching. The :default keyword is
special name used for compatibility with old rulesets.
count Update counters for all packets that match rule. The search con-
tinues with the next rule.
deny | drop
Discard packets that match this rule. The search terminates.
divertport
Divert packets that match this rule to the divert(4) socket bound
to port port. The search terminates.
fwd | forwardipaddr | tablearg[,port]
Change the next-hop on matching packets to ipaddr, which can be
an IP address or a host name. The next hop can also be supplied
by the last table looked up for the packet by using the tablearg
keyword instead of an explicit address. The search terminates if
this rule matches.
If ipaddr is a local address, then matching packets will be for-
warded to port (or the port number in the packet if one is not
specified in the rule) on the local machine.
If ipaddr is not a local address, then the port number (if speci-
fied) is ignored, and the packet will be forwarded to the remote
address, using the route as found in the local routing table for
that IP.
A fwd rule will not match layer-2 packets (those received on
ether_input, ether_output, or bridged).
The fwd action does not change the contents of the packet at all.
In particular, the destination address remains unmodified, so
packets forwarded to another system will usually be rejected by
that system unless there is a matching rule on that system to
capture them. For packets forwarded locally, the local address
of the socket will be set to the original destination address of
the packet. This makes the netstat(1) entry look rather weird
but is intended for use with transparent proxy servers.
natnat_nr | tablearg
Pass packet to a nat instance (for network address translation,
address redirect, etc.): see the NETWORKADDRESSTRANSLATION(NAT) Section for further information.
nat64lsnname
Pass packet to a stateful NAT64 instance (for IPv6/IPv4 network
address and protocol translation): see the IPv6/IPv4NETWORKADDRESSANDPROTOCOLTRANSLATION Section for further information.
nat64stlname
Pass packet to a stateless NAT64 instance (for IPv6/IPv4 network
address and protocol translation): see the IPv6/IPv4NETWORKADDRESSANDPROTOCOLTRANSLATION Section for further information.
nptv6name
Pass packet to a NPTv6 instance (for IPv6-to-IPv6 network prefix
translation): see the IPv6-to-IPv6NETWORKPREFIXTRANSLATION(NPTv6) Section for further information.
pipepipe_nr
Pass packet to a dummynet ``pipe'' (for bandwidth limitation,
delay, etc.). See the TRAFFICSHAPER(DUMMYNET)CONFIGURATION
Section for further information. The search terminates; however,
on exit from the pipe and if the sysctl(8) variable
net.inet.ip.fw.one_pass is not set, the packet is passed again to
the firewall code starting from the next rule.
queuequeue_nr
Pass packet to a dummynet ``queue'' (for bandwidth limitation
using WF2Q+).
reject (Deprecated). Synonym for unreachhost.
reset Discard packets that match this rule, and if the packet is a TCP
packet, try to send a TCP reset (RST) notice. The search termi-
nates.
reset6 Discard packets that match this rule, and if the packet is a TCP
packet, try to send a TCP reset (RST) notice. The search termi-
nates.
skiptonumber | tablearg
Skip all subsequent rules numbered less than number. The search
continues with the first rule numbered number or higher. It is
possible to use the tablearg keyword with a skipto for a computed
skipto. Skipto may work either in O(log(N)) or in O(1) depending
on amount of memory and/or sysctl variables. See the SYSCTLVARIABLES section for more details.
callnumber | tablearg
The current rule number is saved in the internal stack and rule-
set processing continues with the first rule numbered number or
higher. If later a rule with the return action is encountered,
the processing returns to the first rule with number of this call
rule plus one or higher (the same behaviour as with packets
returning from divert(4) socket after a divert action). This
could be used to make somewhat like an assembly language
``subroutine'' calls to rules with common checks for different
interfaces, etc.
Rule with any number could be called, not just forward jumps as
with skipto. So, to prevent endless loops in case of mistakes,
both call and return actions don't do any jumps and simply go to
the next rule if memory cannot be allocated or stack over-
flowed/underflowed.
Internally stack for rule numbers is implemented using
mbuf_tags(9) facility and currently has size of 16 entries. As
mbuf tags are lost when packet leaves the kernel, divert should
not be used in subroutines to avoid endless loops and other unde-
sired effects.
return Takes rule number saved to internal stack by the last call action
and returns ruleset processing to the first rule with number
greater than number of corresponding call rule. See description
of the call action for more details.
Note that return rules usually end a ``subroutine'' and thus are
unconditional, but ipfw command-line utility currently requires
every action except check-state to have body. While it is some-
times useful to return only on some packets, usually you want to
print just ``return'' for readability. A workaround for this is
to use new syntax and -c switch:
# Add a rule without actual body
ipfw add 2999 return via any
# List rules without "from any to any" part
ipfw -c list
This cosmetic annoyance may be fixed in future releases.
teeport
Send a copy of packets matching this rule to the divert(4) socket
bound to port port. The search continues with the next rule.
unreachcode
Discard packets that match this rule, and try to send an ICMP
unreachable notice with code code, where code is a number from 0
to 255, or one of these aliases: net, host, protocol, port,
needfrag, srcfail, net-unknown, host-unknown, isolated,
net-prohib, host-prohib, tosnet, toshost, filter-prohib,
host-precedence or precedence-cutoff. The search terminates.
unreach6code
Discard packets that match this rule, and try to send an ICMPv6
unreachable notice with code code, where code is a number from 0,
1, 3 or 4, or one of these aliases: no-route,admin-prohib,address or port. The search terminates.
netgraphcookie
Divert packet into netgraph with given cookie. The search termi-
nates. If packet is later returned from netgraph it is either
accepted or continues with the next rule, depending on
net.inet.ip.fw.one_pass sysctl variable.
ngteecookie
A copy of packet is diverted into netgraph, original packet con-
tinues with the next rule. See ng_ipfw(4) for more information
on netgraph and ngtee actions.
setfibfibnum | tablearg
The packet is tagged so as to use the FIB (routing table) fibnum
in any subsequent forwarding decisions. In the current implemen-
tation, this is limited to the values 0 through 15, see
setfib(2). Processing continues at the next rule. It is possi-
ble to use the tablearg keyword with setfib. If the tablearg
value is not within the compiled range of fibs, the packet's fib
is set to 0.
setdscpDSCP | number | tablearg
Set specified DiffServ codepoint for an IPv4/IPv6 packet. Pro-
cessing continues at the next rule. Supported values are:
cs0 (000000), cs1 (001000), cs2 (010000), cs3 (011000), cs4
(100000), cs5 (101000), cs6 (110000), cs7 (111000), af11
(001010), af12 (001100), af13 (001110), af21 (010010), af22
(010100), af23 (010110), af31 (011010), af32 (011100), af33
(011110), af41 (100010), af42 (100100), af43 (100110), ef
(101110), be (000000). Additionally, DSCP value can be specified
by number (0..64). It is also possible to use the tablearg key-
word with setdscp. If the tablearg value is not within the 0..64
range, lower 6 bits of supplied value are used.
tcp-setmssmss
Set the Maximum Segment Size (MSS) in the TCP segment to value
mss. The kernel module ipfw_pmod should be loaded or kernel
should have optionsIPFIREWALL_PMOD to be able use this action.
This command does not change a packet if original MSS value is
lower than specified value. Both TCP over IPv4 and over IPv6 are
supported. Regardless of matched a packet or not by the
tcp-setmss rule, the search continues with the next rule.
reass Queue and reassemble IPv4 fragments. If the packet is not frag-
mented, counters are updated and processing continues with the
next rule. If the packet is the last logical fragment, the
packet is reassembled and, if net.inet.ip.fw.one_pass is set to
0, processing continues with the next rule. Otherwise, the
packet is allowed to pass and the search terminates. If the
packet is a fragment in the middle of a logical group of frag-
ments, it is consumed and processing stops immediately.
Fragment handling can be tuned via net.inet.ip.maxfragpackets and
net.inet.ip.maxfragsperpacket which limit, respectively, the max-
imum number of processable fragments (default: 800) and the maxi-
mum number of fragments per packet (default: 16).
NOTA BENE: since fragments do not contain port numbers, they
should be avoided with the reass rule. Alternatively, direction-
based (like in / out ) and source-based (like via ) match pat-
terns can be used to select fragments.
Usually a simple rule like:
# reassemble incoming fragments
ipfw add reass all from any to any in
is all you need at the beginning of your ruleset.
abort Discard packets that match this rule, and if the packet is an
SCTP packet, try to send an SCTP packet containing an ABORT
chunk. The search terminates.
abort6 Discard packets that match this rule, and if the packet is an
SCTP packet, try to send an SCTP packet containing an ABORT
chunk. The search terminates.
RULEBODY
The body of a rule contains zero or more patterns (such as specific
source and destination addresses or ports, protocol options, incoming or
outgoing interfaces, etc.) that the packet must match in order to be
recognised. In general, the patterns are connected by (implicit) and
operators -- i.e., all must match in order for the rule to match. Indi-
vidual patterns can be prefixed by the not operator to reverse the result
of the match, as in
ipfw add 100 allow ip from not 1.2.3.4 to any
Additionally, sets of alternative match patterns (or-blocks) can be con-
structed by putting the patterns in lists enclosed between parentheses (
) or braces { }, and using the or operator as follows:
ipfw add 100 allow ip from { x or not y or z } to any
Only one level of parentheses is allowed. Beware that most shells have
special meanings for parentheses or braces, so it is advisable to put a
backslash \ in front of them to prevent such interpretations.
The body of a rule must in general include a source and destination
address specifier. The keyword any can be used in various places to
specify that the content of a required field is irrelevant.
The rule body has the following format:
[protofromsrctodst] [options]
The first part (proto from src to dst) is for backward compatibility with
earlier versions of FreeBSD. In modern FreeBSD any match pattern
(including MAC headers, IP protocols, addresses and ports) can be speci-
fied in the options section.
Rule fields have the following meaning:
proto: protocol | {protocolor...}protocol: [not] protocol-name | protocol-number
An IP protocol specified by number or name (for a complete list
see /etc/protocols), or one of the following keywords:
ip4 | ipv4
Matches IPv4 packets.
ip6 | ipv6
Matches IPv6 packets.
ip | all
Matches any packet.
The ipv6 in proto option will be treated as inner protocol. And,
the ipv4 is not available in proto option.
The {protocolor...} format (an or-block) is provided for con-
venience only but its use is deprecated.
src and dst: {addr | {addror...}} [[not] ports]
An address (or a list, see below) optionally followed by ports
specifiers.
The second format (or-block with multiple addresses) is provided
for convenience only and its use is discouraged.
addr: [not] {any | me | me6 | table(name[,value]) | addr-list | addr-set}
any matches any IP address.
me matches any IP address configured on an interface in the
system.
me6 matches any IPv6 address configured on an interface in
the system. The address list is evaluated at the time
the packet is analysed.
table(name[,value])
Matches any IPv4 or IPv6 address for which an entry
exists in the lookup table number. If an optional 32-bit
unsigned value is also specified, an entry will match
only if it has this value. See the LOOKUPTABLES section
below for more information on lookup tables.
addr-list: ip-addr[,addr-list]
ip-addr:
A host or subnet address specified in one of the following ways:
numeric-ip | hostname
Matches a single IPv4 address, specified as dotted-quad
or a hostname. Hostnames are resolved at the time the
rule is added to the firewall list.
addr/masklen
Matches all addresses with base addr (specified as an IP
address, a network number, or a hostname) and mask width
of masklen bits. As an example, 1.2.3.4/25 or 1.2.3.0/25
will match all IP numbers from 1.2.3.0 to 1.2.3.127 .
addr:mask
Matches all addresses with base addr (specified as an IP
address, a network number, or a hostname) and the mask of
mask, specified as a dotted quad. As an example,
1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match
1.*.3.*. This form is advised only for non-contiguous
masks. It is better to resort to the addr/masklen format
for contiguous masks, which is more compact and less
error-prone.
addr-set: addr[/masklen]{list}list: {num | num-num}[,list]
Matches all addresses with base address addr (specified as an IP
address, a network number, or a hostname) and whose last byte is
in the list between braces { } . Note that there must be no spa-
ces between braces and numbers (spaces after commas are allowed).
Elements of the list can be specified as single entries or
ranges. The masklen field is used to limit the size of the set
of addresses, and can have any value between 24 and 32. If not
specified, it will be assumed as 24.
This format is particularly useful to handle sparse address sets
within a single rule. Because the matching occurs using a bit-
mask, it takes constant time and dramatically reduces the com-
plexity of rulesets.
As an example, an address specified as 1.2.3.4/24{128,35-55,89}
or 1.2.3.0/24{128,35-55,89} will match the following IP
addresses:
1.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 .
addr6-list: ip6-addr[,addr6-list]
ip6-addr:
A host or subnet specified one of the following ways:
numeric-ip | hostname
Matches a single IPv6 address as allowed by inet_pton(3)
or a hostname. Hostnames are resolved at the time the
rule is added to the firewall list.
addr/masklen
Matches all IPv6 addresses with base addr (specified as
allowed by inet_pton or a hostname) and mask width of
masklen bits.
addr/mask
Matches all IPv6 addresses with base addr (specified as
allowed by inet_pton or a hostname) and the mask of mask,
specified as allowed by inet_pton. As an example,
fe::640:0:0/ffff::ffff:ffff:0:0 will match
fe:*:*:*:0:640:*:*. This form is advised only for non-
contiguous masks. It is better to resort to the
addr/masklen format for contiguous masks, which is more
compact and less error-prone.
No support for sets of IPv6 addresses is provided because IPv6
addresses are typically random past the initial prefix.
ports: {port | port-port}[,ports]
For protocols which support port numbers (such as SCTP, TCP and
UDP), optional ports may be specified as one or more ports or
port ranges, separated by commas but no spaces, and an optional
not operator. The `-' notation specifies a range of ports
(including boundaries).
Service names (from /etc/services) may be used instead of numeric
port values. The length of the port list is limited to 30 ports
or ranges, though one can specify larger ranges by using an
or-block in the options section of the rule.
A backslash (`\') can be used to escape the dash (`-') character
in a service name (from a shell, the backslash must be typed
twice to avoid the shell itself interpreting it as an escape
character).
ipfw add count tcp from any ftp\\-data-ftp to any
Fragmented packets which have a non-zero offset (i.e., not the
first fragment) will never match a rule which has one or more
port specifications. See the frag option for details on matching
fragmented packets.
RULEOPTIONS(MATCHPATTERNS)
Additional match patterns can be used within rules. Zero or more of
these so-called options can be present in a rule, optionally prefixed by
the not operand, and possibly grouped into or-blocks.
The following match patterns can be used (listed in alphabetical order):
//thisisacomment.
Inserts the specified text as a comment in the rule. Everything
following // is considered as a comment and stored in the rule.
You can have comment-only rules, which are listed as having a
count action followed by the comment.
bridged
Alias for layer2.
diverted
Matches only packets generated by a divert socket.
diverted-loopback
Matches only packets coming from a divert socket back into the IP
stack input for delivery.
diverted-output
Matches only packets going from a divert socket back outward to
the IP stack output for delivery.
dst-ipip-address
Matches IPv4 packets whose destination IP is one of the
address(es) specified as argument.
{dst-ip6 | dst-ipv6} ip6-address
Matches IPv6 packets whose destination IP is one of the
address(es) specified as argument.
dst-portports
Matches IP packets whose destination port is one of the port(s)
specified as argument.
established
Matches TCP packets that have the RST or ACK bits set.
ext6hdrheader
Matches IPv6 packets containing the extended header given by
header. Supported headers are:
Fragment, (frag), Hop-to-hop options (hopopt), any type of Rout-
ing Header (route), Source routing Routing Header Type 0
(rthdr0), Mobile IPv6 Routing Header Type 2 (rthdr2), Destination
options (dstopt), IPSec authentication headers (ah), and IPsec
encapsulated security payload headers (esp).
fibfibnum
Matches a packet that has been tagged to use the given FIB (rout-
ing table) number.
flowtable(name[,value])
Search for the flow entry in lookup table name. If not found,
the match fails. Otherwise, the match succeeds and tablearg is
set to the value extracted from the table.
This option can be useful to quickly dispatch traffic based on
certain packet fields. See the LOOKUPTABLES section below for
more information on lookup tables.
flow-idlabels
Matches IPv6 packets containing any of the flow labels given in
labels. labels is a comma separated list of numeric flow labels.
frag Matches packets that are fragments and not the first fragment of
an IP datagram. Note that these packets will not have the next
protocol header (e.g. TCP, UDP) so options that look into these
headers cannot match.
gidgroup
Matches all TCP or UDP packets sent by or received for a group.
A group may be specified by name or number.
jailprisonID
Matches all TCP or UDP packets sent by or received for the jail
whos prison ID is prisonID.
icmptypestypes
Matches ICMP packets whose ICMP type is in the list types. The
list may be specified as any combination of individual types
(numeric) separated by commas. Rangesarenotallowed. The sup-
ported ICMP types are:
echo reply (0), destination unreachable (3), source quench (4),
redirect (5), echo request (8), router advertisement (9), router
solicitation (10), time-to-live exceeded (11), IP header bad
(12), timestamp request (13), timestamp reply (14), information
request (15), information reply (16), address mask request (17)
and address mask reply (18).
icmp6typestypes
Matches ICMP6 packets whose ICMP6 type is in the list of types.
The list may be specified as any combination of individual types
(numeric) separated by commas. Rangesarenotallowed.
in | out
Matches incoming or outgoing packets, respectively. in and out
are mutually exclusive (in fact, out is implemented as notin).
ipidid-list
Matches IPv4 packets whose ip_id field has value included in
id-list, which is either a single value or a list of values or
ranges specified in the same way as ports.
iplenlen-list
Matches IP packets whose total length, including header and data,
is in the set len-list, which is either a single value or a list
of values or ranges specified in the same way as ports.
ipoptionsspec
Matches packets whose IPv4 header contains the comma separated
list of options specified in spec. The supported IP options are:
ssrr (strict source route), lsrr (loose source route), rr (record
packet route) and ts (timestamp). The absence of a particular
option may be denoted with a `!'.
ipprecedenceprecedence
Matches IPv4 packets whose precedence field is equal to
precedence.
ipsec Matches packets that have IPSEC history associated with them
(i.e., the packet comes encapsulated in IPSEC, the kernel has
IPSEC support, and can correctly decapsulate it).
Note that specifying ipsec is different from specifying protoipsec as the latter will only look at the specific IP protocol
field, irrespective of IPSEC kernel support and the validity of
the IPSEC data.
Further note that this flag is silently ignored in kernels with-
out IPSEC support. It does not affect rule processing when given
and the rules are handled as if with no ipsec flag.
iptosspec
Matches IPv4 packets whose tos field contains the comma separated
list of service types specified in spec. The supported IP types
of service are:
lowdelay (IPTOS_LOWDELAY), throughput (IPTOS_THROUGHPUT),
reliability (IPTOS_RELIABILITY), mincost (IPTOS_MINCOST),
congestion (IPTOS_ECN_CE). The absence of a particular type may
be denoted with a `!'.
dscpspec[,spec]
Matches IPv4/IPv6 packets whose DS field value is contained in
spec mask. Multiple values can be specified via the comma sepa-
rated list. Value can be one of keywords used in setdscp action
or exact number.
ipttlttl-list
Matches IPv4 packets whose time to live is included in ttl-list,
which is either a single value or a list of values or ranges
specified in the same way as ports.
ipversionver
Matches IP packets whose IP version field is ver.
keep-state [:flowname]
Upon a match, the firewall will create a dynamic rule, whose
default behaviour is to match bidirectional traffic between
source and destination IP/port using the same protocol. The rule
has a limited lifetime (controlled by a set of sysctl(8) vari-
ables), and the lifetime is refreshed every time a matching
packet is found. The :flowname is used to assign additional to
addresses, ports and protocol parameter to dynamic rule. It can
be used for more accurate matching by check-state rule. The
:default keyword is special name used for compatibility with old
rulesets.
layer2 Matches only layer2 packets, i.e., those passed to ipfw from
ether_demux() and ether_output_frame().
limit {src-addr | src-port | dst-addr | dst-port} N [:flowname]
The firewall will only allow N connections with the same set of
parameters as specified in the rule. One or more of source and
destination addresses and ports can be specified.
lookup {dst-ip | dst-port | src-ip | src-port | uid | jail} name
Search an entry in lookup table name that matches the field spec-
ified as argument. If not found, the match fails. Otherwise,
the match succeeds and tablearg is set to the value extracted
from the table.
This option can be useful to quickly dispatch traffic based on
certain packet fields. See the LOOKUPTABLES section below for
more information on lookup tables.
{MAC | mac}dst-macsrc-mac
Match packets with a given dst-mac and src-mac addresses, speci-
fied as the any keyword (matching any MAC address), or six groups
of hex digits separated by colons, and optionally followed by a
mask indicating the significant bits. The mask may be specified
using either of the following methods:
1. A slash (/) followed by the number of significant bits.
For example, an address with 33 significant bits could be
specified as:
MAC 10:20:30:40:50:60/33 any
2. An ampersand (&) followed by a bitmask specified as six
groups of hex digits separated by colons. For example,
an address in which the last 16 bits are significant
could be specified as:
MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any
Note that the ampersand character has a special meaning
in many shells and should generally be escaped.
Note that the order of MAC addresses (destination first, source
second) is the same as on the wire, but the opposite of the one
used for IP addresses.
mac-typemac-type
Matches packets whose Ethernet Type field corresponds to one of
those specified as argument. mac-type is specified in the same
way as portnumbers (i.e., one or more comma-separated single
values or ranges). You can use symbolic names for known values
such as vlan, ipv4,ipv6. Values can be entered as decimal or
hexadecimal (if prefixed by 0x), and they are always printed as
hexadecimal (unless the -N option is used, in which case symbolic
resolution will be attempted).
protoprotocol
Matches packets with the corresponding IP protocol.
recv | xmit | via {ifX | if* | table(name[,value]) | ipno | any}
Matches packets received, transmitted or going through, respec-
tively, the interface specified by exact name (ifX), by device
name (if*), by IP address, or through some interface. Table name
may be used to match interface by its kernel ifindex. See the
LOOKUPTABLES section below for more information on lookup
tables.
The via keyword causes the interface to always be checked. If
recv or xmit is used instead of via, then only the receive or
transmit interface (respectively) is checked. By specifying
both, it is possible to match packets based on both receive and
transmit interface, e.g.:
ipfw add deny ip from any to any out recv ed0 xmit ed1
The recv interface can be tested on either incoming or outgoing
packets, while the xmit interface can only be tested on outgoing
packets. So out is required (and in is invalid) whenever xmit is
used.
A packet might not have a receive or transmit interface: packets
originating from the local host have no receive interface, while
packets destined for the local host have no transmit interface.
setup Matches TCP packets that have the SYN bit set but no ACK bit.
This is the short form of ``tcpflags syn,!ack''.
sockarg
Matches packets that are associated to a local socket and for
which the SO_USER_COOKIE socket option has been set to a non-zero
value. As a side effect, the value of the option is made avail-
able as tablearg value, which in turn can be used as skipto or
pipe number.
src-ipip-address
Matches IPv4 packets whose source IP is one of the address(es)
specified as an argument.
src-ip6ip6-address
Matches IPv6 packets whose source IP is one of the address(es)
specified as an argument.
src-portports
Matches IP packets whose source port is one of the port(s) speci-
fied as argument.
taggedtag-list
Matches packets whose tags are included in tag-list, which is
either a single value or a list of values or ranges specified in
the same way as ports. Tags can be applied to the packet using
tag rule action parameter (see it's description for details on
tags).
tcpackack
TCP packets only. Match if the TCP header acknowledgment number
field is set to ack.
tcpdatalentcpdatalen-list
Matches TCP packets whose length of TCP data is tcpdatalen-list,
which is either a single value or a list of values or ranges
specified in the same way as ports.
tcpflagsspec
TCP packets only. Match if the TCP header contains the comma
separated list of flags specified in spec. The supported TCP
flags are:
fin, syn, rst, psh, ack and urg. The absence of a particular
flag may be denoted with a `!'. A rule which contains a tcpflags
specification can never match a fragmented packet which has a
non-zero offset. See the frag option for details on matching
fragmented packets.
tcpseqseq
TCP packets only. Match if the TCP header sequence number field
is set to seq.
tcpwintcpwin-list
Matches TCP packets whose header window field is set to
tcpwin-list, which is either a single value or a list of values
or ranges specified in the same way as ports.
tcpoptionsspec
TCP packets only. Match if the TCP header contains the comma
separated list of options specified in spec. The supported TCP
options are:
mss (maximum segment size), window (tcp window advertisement),
sack (selective ack), ts (rfc1323 timestamp) and cc (rfc1644
t/tcp connection count). The absence of a particular option may
be denoted with a `!'.
uiduser
Match all TCP or UDP packets sent by or received for a user. A
user may be matched by name or identification number.
verrevpath
For incoming packets, a routing table lookup is done on the
packet's source address. If the interface on which the packet
entered the system matches the outgoing interface for the route,
the packet matches. If the interfaces do not match up, the
packet does not match. All outgoing packets or packets with no
incoming interface match.
The name and functionality of the option is intentionally similar
to the Cisco IOS command:
ip verify unicast reverse-path
This option can be used to make anti-spoofing rules to reject all
packets with source addresses not from this interface. See also
the option antispoof.
versrcreach
For incoming packets, a routing table lookup is done on the
packet's source address. If a route to the source address
exists, but not the default route or a blackhole/reject route,
the packet matches. Otherwise, the packet does not match. All
outgoing packets match.
The name and functionality of the option is intentionally similar
to the Cisco IOS command:
ip verify unicast source reachable-via any
This option can be used to make anti-spoofing rules to reject all
packets whose source address is unreachable.
antispoof
For incoming packets, the packet's source address is checked if
it belongs to a directly connected network. If the network is
directly connected, then the interface the packet came on in is
compared to the interface the network is connected to. When
incoming interface and directly connected interface are not the
same, the packet does not match. Otherwise, the packet does
match. All outgoing packets match.
This option can be used to make anti-spoofing rules to reject all
packets that pretend to be from a directly connected network but
do not come in through that interface. This option is similar to
but more restricted than verrevpath because it engages only on
packets with source addresses of directly connected networks
instead of all source addresses.
LOOKUP TABLES
Lookup tables are useful to handle large sparse sets of addresses or
other search keys (e.g., ports, jail IDs, interface names). In the rest
of this section we will use the term ``key''. Table name needs to match
the following spec: table-name. Tables with the same name can be created
in different sets. However, rule links to the tables in set0 by
default. This behavior can be controlled by net.inet.ip.fw.tables_sets
variable. See the SETSOFRULES section for more information. There may
be up to 65535 different lookup tables.
The following table types are supported:
table-type: addr | iface | number | flowtable-key: addr[/masklen] | iface-name | number | flow-spec
flow-spec: flow-field[,flow-spec]
flow-field: src-ip | proto | src-port | dst-ip | dst-portaddr matches IPv4 or IPv6 address. Each entry is represented by an
addr[/masklen] and will match all addresses with base addr (spec-
ified as an IPv4/IPv6 address, or a hostname) and mask width of
masklen bits. If masklen is not specified, it defaults to 32 for
IPv4 and 128 for IPv6. When looking up an IP address in a table,
the most specific entry will match.
iface matches interface names. Each entry is represented by string
treated as interface name. Wildcards are not supported.
number maches protocol ports, uids/gids or jail IDs. Each entry is rep-
resented by 32-bit unsigned integer. Ranges are not supported.
flow Matches packet fields specified by flow type suboptions with ta-
ble entries.
Tables require explicit creation via create before use.
The following creation options are supported:
create-options: create-option | create-optionscreate-option: typetable-type | valtypevalue-mask | algoalgo-desc |
limitnumber | lockedtype Table key type.
valtype
Table value mask.
algo Table algorithm to use (see below).
limit Maximum number of items that may be inserted into table.
locked Restrict any table modifications.
Some of these options may be modified later via modify keyword. The fol-
lowing options can be changed:
modify-options: modify-option | modify-optionsmodify-option: limitnumberlimit Alter maximum number of items that may be inserted into table.
Additionally, table can be locked or unlocked using lock or unlock com-
mands.
Tables of the same type can be swapped with each other using swapname
command. Swap may fail if tables limits are set and data exchange would
result in limits hit. Operation is performed atomically.
One or more entries can be added to a table at once using add command.
Addition of all items are performed atomically. By default, error in
addition of one entry does not influence addition of other entries. How-
ever, non-zero error code is returned in that case. Special atomic key-
word may be specified before add to indicate all-or-none add request.
One or more entries can be removed from a table at once using delete com-
mand. By default, error in removal of one entry does not influence
removing of other entries. However, non-zero error code is returned in
that case.
It may be possible to check what entry will be found on particular
table-key using lookuptable-key command. This functionality is optional
and may be unsupported in some algorithms.
The following operations can be performed on one or all tables:
list List all entries.
flush Removes all entries.
info Shows generic table information.
detail Shows generic table information and algo-specific data.
The following lookup algorithms are supported:
algo-desc: algo-name | algo-namealgo-dataalgo-name:addr:radix | addr:hash | iface:array | number:array |
flow:hashaddr:radix
Separate Radix trees for IPv4 and IPv6, the same way as the rout-
ing table (see route(4)). Default choice for addr type.
addr:hash
Separate auto-growing hashes for IPv4 and IPv6. Accepts entries
with the same mask length specified initially via addr:hashmasks=/v4,/v6 algorithm creation options. Assume /32 and /128
masks by default. Search removes host bits (according to mask)
from supplied address and checks resulting key in appropriate
hash. Mostly optimized for /64 and byte-ranged IPv6 masks.
iface:array
Array storing sorted indexes for entries which are presented in
the system. Optimized for very fast lookup.
number:array
Array storing sorted u32 numbers.
flow:hash
Auto-growing hash storing flow entries. Search calculates hash
on required packet fields and searches for matching entries in
selected bucket.
The tablearg feature provides the ability to use a value, looked up in
the table, as the argument for a rule action, action parameter or rule
option. This can significantly reduce number of rules in some configura-
tions. If two tables are used in a rule, the result of the second (des-
tination) is used.
Each record may hold one or more values according to value-mask. This
mask is set on table creation via valtype option. The following value
types are supported:
value-mask: value-type[,value-mask]
value-type: skipto | pipe | fib | nat | dscp | tag | divert |
netgraph | limit | ipv4skipto rule number to jump to.
pipe Pipe number to use.
fib fib number to match/set.
nat nat number to jump to.
dscp dscp value to match/set.
tag tag number to match/set.
divert port number to divert traffic to.
netgraph
hook number to move packet to.
limit maximum number of connections.
ipv4 IPv4 nexthop to fwd packets to.
ipv6 IPv6 nexthop to fwd packets to.
The tablearg argument can be used with the following actions: nat,pipe,
queue,divert,tee,netgraph,ngtee,fwd,skipto,setfib, action parame-
ters: tag,untag, rule options: limit,tagged.
When used with the skipto action, the user should be aware that the code
will walk the ruleset up to a rule equal to, or past, the given number.
See the EXAMPLES Section for example usage of tables and the tablearg
keyword.
SETS OF RULES
Each rule or table belongs to one of 32 different sets , numbered 0 to
31. Set 31 is reserved for the default rule.
By default, rules or tables are put in set 0, unless you use the setN
attribute when adding a new rule or table. Sets can be individually and
atomically enabled or disabled, so this mechanism permits an easy way to
store multiple configurations of the firewall and quickly (and atomi-
cally) switch between them.
By default, tables from set 0 are referenced when adding rule with table
opcodes regardless of rule set. This behavior can be changed by setting
net.inet.ip.fw.tables_sets variable to 1. Rule's set will then be used
for table references.
The command to enable/disable sets is
ipfwset [disablenumber...] [enablenumber...]
where multiple enable or disable sections can be specified. Command exe-
cution is atomic on all the sets specified in the command. By default,
all sets are enabled.
When you disable a set, its rules behave as if they do not exist in the
firewall configuration, with only one exception:
dynamic rules created from a rule before it had been disabled will
still be active until they expire. In order to delete dynamic
rules you have to explicitly delete the parent rule which generated
them.
The set number of rules can be changed with the command
ipfwsetmove {rulerule-number | old-set} tonew-set
Also, you can atomically swap two rulesets with the command
ipfwsetswapfirst-setsecond-set
See the EXAMPLES Section on some possible uses of sets of rules.
STATEFUL FIREWALL
Stateful operation is a way for the firewall to dynamically create rules
for specific flows when packets that match a given pattern are detected.
Support for stateful operation comes through the check-state, keep-state
and limit options of rules.
Dynamic rules are created when a packet matches a keep-state or limit
rule, causing the creation of a dynamic rule which will match all and
only packets with a given protocol between a src-ip/src-portdst-ip/dst-port pair of addresses (src and dst are used here only to
denote the initial match addresses, but they are completely equivalent
afterwards). Rules created by keep-state option also have a :flowname
taken from it. This name is used in matching together with addresses,
ports and protocol. Dynamic rules will be checked at the first
check-state,keep-state or limit occurrence, and the action performed
upon a match will be the same as in the parent rule.
Note that no additional attributes other than protocol and IP addresses
and ports and :flowname are checked on dynamic rules.
The typical use of dynamic rules is to keep a closed firewall configura-
tion, but let the first TCP SYN packet from the inside network install a
dynamic rule for the flow so that packets belonging to that session will
be allowed through the firewall:
ipfw add check-state :OUTBOUND
ipfw add allow tcp from my-subnet to any setup keep-state :OUTBOUND
ipfw add deny tcp from any to any
A similar approach can be used for UDP, where an UDP packet coming from
the inside will install a dynamic rule to let the response through the
firewall:
ipfw add check-state :OUTBOUND
ipfw add allow udp from my-subnet to any keep-state :OUTBOUND
ipfw add deny udp from any to any
Dynamic rules expire after some time, which depends on the status of the
flow and the setting of some sysctl variables. See Section SYSCTLVARIABLES for more details. For TCP sessions, dynamic rules can be
instructed to periodically send keepalive packets to refresh the state of
the rule when it is about to expire.
See Section EXAMPLES for more examples on how to use dynamic rules.
TRAFFIC SHAPER (DUMMYNET) CONFIGURATIONipfw is also the user interface for the dummynet traffic shaper, packet
scheduler and network emulator, a subsystem that can artificially queue,
delay or drop packets emulating the behaviour of certain network links or
queueing systems.
dummynet operates by first using the firewall to select packets using any
match pattern that can be used in ipfw rules. Matching packets are then
passed to either of two different objects, which implement the traffic
regulation:
pipe A pipe emulates a link with given bandwidth and propagation
delay, driven by a FIFO scheduler and a single queue with
programmable queue size and packet loss rate. Packets are
appended to the queue as they come out from ipfw, and then
transferred in FIFO order to the link at the desired rate.
queue A queue is an abstraction used to implement packet scheduling
using one of several packet scheduling algorithms. Packets
sent to a queue are first grouped into flows according to a
mask on the 5-tuple. Flows are then passed to the scheduler
associated to the queue, and each flow uses scheduling param-
eters (weight and others) as configured in the queue itself.
A scheduler in turn is connected to an emulated link, and
arbitrates the link's bandwidth among backlogged flows
according to weights and to the features of the scheduling
algorithm in use.
In practice, pipes can be used to set hard limits to the bandwidth that a
flow can use, whereas queues can be used to determine how different flows
share the available bandwidth.
A graphical representation of the binding of queues, flows, schedulers
and links is below.
(flow_mask|sched_mask) sched_mask
+---------+ weight Wx +-------------+
| |->-[flow]-->--| |-+
-->--| QUEUE x | ... | | |
| |->-[flow]-->--| SCHEDuler N | |
+---------+ | | |
... | +--[LINK N]-->--
+---------+ weight Wy | | +--[LINK N]-->--
| |->-[flow]-->--| | |
-->--| QUEUE y | ... | | |
| |->-[flow]-->--| | |
+---------+ +-------------+ |
+-------------+
It is important to understand the role of the SCHED_MASK and FLOW_MASK,
which are configured through the commands
ipfw sched N config mask SCHED_MASK ...
and
ipfw queue X config mask FLOW_MASK ....
The SCHED_MASK is used to assign flows to one or more scheduler
instances, one for each value of the packet's 5-tuple after applying
SCHED_MASK. As an example, using ``src-ip 0xffffff00'' creates one
instance for each /24 destination subnet.
The FLOW_MASK, together with the SCHED_MASK, is used to split packets
into flows. As an example, using ``src-ip 0x000000ff'' together with the
previous SCHED_MASK makes a flow for each individual source address. In
turn, flows for each /24 subnet will be sent to the same scheduler
instance.
The above diagram holds even for the pipe case, with the only restriction
that a pipe only supports a SCHED_MASK, and forces the use of a FIFO
scheduler (these are for backward compatibility reasons; in fact, inter-
nally, a dummynet's pipe is implemented exactly as above).
There are two modes of dummynet operation: ``normal'' and ``fast''. The
``normal'' mode tries to emulate a real link: the dummynet scheduler
ensures that the packet will not leave the pipe faster than it would on
the real link with a given bandwidth. The ``fast'' mode allows certain
packets to bypass the dummynet scheduler (if packet flow does not exceed
pipe's bandwidth). This is the reason why the ``fast'' mode requires
less CPU cycles per packet (on average) and packet latency can be signif-
icantly lower in comparison to a real link with the same bandwidth. The
default mode is ``normal''. The ``fast'' mode can be enabled by setting
the net.inet.ip.dummynet.io_fastsysctl(8) variable to a non-zero value.
PIPE,QUEUEANDSCHEDULERCONFIGURATION
The pipe, queue and scheduler configuration commands are the following:
pipenumberconfigpipe-configurationqueuenumberconfigqueue-configurationschednumberconfigsched-configuration
The following parameters can be configured for a pipe:
bwbandwidth | device
Bandwidth, measured in [K|M|G]{bit/s|Byte/s}.
A value of 0 (default) means unlimited bandwidth. The unit must
immediately follow the number, as in
ipfw pipe 1 config bw 300Kbit/s
If a device name is specified instead of a numeric value, as in
ipfw pipe 1 config bw tun0
then the transmit clock is supplied by the specified device. At
the moment only the tun(4) device supports this functionality,
for use in conjunction with ppp(8).
delayms-delay
Propagation delay, measured in milliseconds. The value is
rounded to the next multiple of the clock tick (typically 10ms,
but it is a good practice to run kernels with ``options HZ=1000''
to reduce the granularity to 1ms or less). The default value is
0, meaning no delay.
burstsize
If the data to be sent exceeds the pipe's bandwidth limit (and
the pipe was previously idle), up to size bytes of data are
allowed to bypass the dummynet scheduler, and will be sent as
fast as the physical link allows. Any additional data will be
transmitted at the rate specified by the pipe bandwidth. The
burst size depends on how long the pipe has been idle; the effec-
tive burst size is calculated as follows: MAX( size , bw *
pipe_idle_time).
profilefilename
A file specifying the additional overhead incurred in the trans-
mission of a packet on the link.
Some link types introduce extra delays in the transmission of a
packet, e.g., because of MAC level framing, contention on the use
of the channel, MAC level retransmissions and so on. From our
point of view, the channel is effectively unavailable for this
extra time, which is constant or variable depending on the link
type. Additionally, packets may be dropped after this time
(e.g., on a wireless link after too many retransmissions). We
can model the additional delay with an empirical curve that rep-
resents its distribution.
cumulative probability
1.0 ^
|
L +-- loss-level x
| ******
| *
| *****
| *
| **
| *
+-------*------------------->
delay
The empirical curve may have both vertical and horizontal lines.
Vertical lines represent constant delay for a range of probabili-
ties. Horizontal lines correspond to a discontinuity in the
delay distribution: the pipe will use the largest delay for a
given probability.
The file format is the following, with whitespace acting as a
separator and '#' indicating the beginning a comment:
nameidentifier
optional name (listed by "ipfw pipe show") to identify
the delay distribution;
bwvalue
the bandwidth used for the pipe. If not specified here,
it must be present explicitly as a configuration parame-
ter for the pipe;
loss-levelL
the probability above which packets are lost. (0.0 <= L
<= 1.0, default 1.0 i.e., no loss);
samplesN
the number of samples used in the internal representation
of the curve (2..1024; default 100);
delayprob | probdelay
One of these two lines is mandatory and defines the for-
mat of the following lines with data points.
XXXYYY
2 or more lines representing points in the curve, with
either delay or probability first, according to the cho-
sen format. The unit for delay is milliseconds. Data
points do not need to be sorted. Also, the number of
actual lines can be different from the value of the "sam-
ples" parameter: ipfw utility will sort and interpolate
the curve as needed.
Example of a profile file:
name bla_bla_bla
samples 100
loss-level 0.86
prob delay
0 200 # minimum overhead is 200ms
0.5 200
0.5 300
0.8 1000
0.9 1300
1 1300
#configuration file end
The following parameters can be configured for a queue:
pipepipe_nr
Connects a queue to the specified pipe. Multiple queues (with
the same or different weights) can be connected to the same pipe,
which specifies the aggregate rate for the set of queues.
weightweight
Specifies the weight to be used for flows matching this queue.
The weight must be in the range 1..100, and defaults to 1.
The following case-insensitive parameters can be configured for a sched-
uler:
type{fifo | wf2q+ | rr | qfq}
specifies the scheduling algorithm to use.
fifo is just a FIFO scheduler (which means that all packets
are stored in the same queue as they arrive to the sched-
uler). FIFO has O(1) per-packet time complexity, with
very low constants (estimate 60-80ns on a 2GHz desktop
machine) but gives no service guarantees.
wf2q+ implements the WF2Q+ algorithm, which is a Weighted Fair
Queueing algorithm which permits flows to share bandwidth
according to their weights. Note that weights are not
priorities; even a flow with a minuscule weight will
never starve. WF2Q+ has O(log N) per-packet processing
cost, where N is the number of flows, and is the default
algorithm used by previous versions dummynet's queues.
rr implements the Deficit Round Robin algorithm, which has
O(1) processing costs (roughly, 100-150ns per packet) and
permits bandwidth allocation according to weights, but
with poor service guarantees.
qfq implements the QFQ algorithm, which is a very fast vari-
ant of WF2Q+, with similar service guarantees and O(1)
processing costs (roughly, 200-250ns per packet).
In addition to the type, all parameters allowed for a pipe can also be
specified for a scheduler.
Finally, the following parameters can be configured for both pipes and
queues:
bucketshash-table-size
Specifies the size of the hash table used for storing the various
queues. Default value is 64 controlled by the sysctl(8) variable
net.inet.ip.dummynet.hash_size, allowed range is 16 to 65536.
maskmask-specifier
Packets sent to a given pipe or queue by an ipfw rule can be fur-
ther classified into multiple flows, each of which is then sent to
a different dynamic pipe or queue. A flow identifier is con-
structed by masking the IP addresses, ports and protocol types as
specified with the mask options in the configuration of the pipe or
queue. For each different flow identifier, a new pipe or queue is
created with the same parameters as the original object, and match-
ing packets are sent to it.
Thus, when dynamicpipes are used, each flow will get the same
bandwidth as defined by the pipe, whereas when dynamicqueues are
used, each flow will share the parent's pipe bandwidth evenly with
other flows generated by the same queue (note that other queues
with different weights might be connected to the same pipe).
Available mask specifiers are a combination of one or more of the
following:
dst-ipmask, dst-ip6mask, src-ipmask, src-ip6mask, dst-portmask, src-portmask, flow-idmask, protomask or all,
where the latter means all bits in all fields are significant.
noerror
When a packet is dropped by a dummynet queue or pipe, the error is
normally reported to the caller routine in the kernel, in the same
way as it happens when a device queue fills up. Setting this
option reports the packet as successfully delivered, which can be
needed for some experimental setups where you want to simulate loss
or congestion at a remote router.
plrpacket-loss-rate
Packet loss rate. Argument packet-loss-rate is a floating-point
number between 0 and 1, with 0 meaning no loss, 1 meaning 100%
loss. The loss rate is internally represented on 31 bits.
queue {slots | sizeKbytes}
Queue size, in slots or KBytes. Default value is 50 slots, which
is the typical queue size for Ethernet devices. Note that for slow
speed links you should keep the queue size short or your traffic
might be affected by a significant queueing delay. E.g., 50 max-
sized ethernet packets (1500 bytes) mean 600Kbit or 20s of queue on
a 30Kbit/s pipe. Even worse effects can result if you get packets
from an interface with a much larger MTU, e.g. the loopback inter-
face with its 16KB packets. The sysctl(8) variables
net.inet.ip.dummynet.pipe_byte_limit and
net.inet.ip.dummynet.pipe_slot_limit control the maximum lengths
that can be specified.
red | gredw_q/min_th/max_th/max_p
[ecn] Make use of the RED (Random Early Detection) queue management
algorithm. w_q and max_p are floating point numbers between 0 and
1 (inclusive), while min_th and max_th are integer numbers specify-
ing thresholds for queue management (thresholds are computed in
bytes if the queue has been defined in bytes, in slots otherwise).
The two parameters can also be of the same value if needed. The
dummynet also supports the gentle RED variant (gred) and ECN
(Explicit Congestion Notification) as optional. Three sysctl(8)
variables can be used to control the RED behaviour:
net.inet.ip.dummynet.red_lookup_depth
specifies the accuracy in computing the average queue when
the link is idle (defaults to 256, must be greater than
zero)
net.inet.ip.dummynet.red_avg_pkt_size
specifies the expected average packet size (defaults to
512, must be greater than zero)
net.inet.ip.dummynet.red_max_pkt_size
specifies the expected maximum packet size, only used when
queue thresholds are in bytes (defaults to 1500, must be
greater than zero).
When used with IPv6 data, dummynet currently has several limitations.
Information necessary to route link-local packets to an interface is not
available after processing by dummynet so those packets are dropped in
the output path. Care should be taken to ensure that link-local packets
are not passed to dummynet.
CHECKLIST
Here are some important points to consider when designing your rules:
+o Remember that you filter both packets going in and out. Most connec-
tions need packets going in both directions.
+o Remember to test very carefully. It is a good idea to be near the
console when doing this. If you cannot be near the console, use an
auto-recovery script such as the one in
/usr/share/examples/ipfw/change_rules.sh.
+o Do not forget the loopback interface.
FINE POINTS+o There are circumstances where fragmented datagrams are uncondition-
ally dropped. TCP packets are dropped if they do not contain at
least 20 bytes of TCP header, UDP packets are dropped if they do not
contain a full 8 byte UDP header, and ICMP packets are dropped if
they do not contain 4 bytes of ICMP header, enough to specify the
ICMP type, code, and checksum. These packets are simply logged as
``pullup failed'' since there may not be enough good data in the
packet to produce a meaningful log entry.
+o Another type of packet is unconditionally dropped, a TCP packet with
a fragment offset of one. This is a valid packet, but it only has
one use, to try to circumvent firewalls. When logging is enabled,
these packets are reported as being dropped by rule -1.
+o If you are logged in over a network, loading the kld(4) version of
ipfw is probably not as straightforward as you would think. The fol-
lowing command line is recommended:
kldload ipfw && \
ipfw add 32000 allow ip from any to any
Along the same lines, doing an
ipfw flush
in similar surroundings is also a bad idea.
+o The ipfw filter list may not be modified if the system security level
is set to 3 or higher (see init(8) for information on system security
levels).
PACKET DIVERSION
A divert(4) socket bound to the specified port will receive all packets
diverted to that port. If no socket is bound to the destination port, or
if the divert module is not loaded, or if the kernel was not compiled
with divert socket support, the packets are dropped.
NETWORK ADDRESS TRANSLATION (NAT)ipfw support in-kernel NAT using the kernel version of libalias(3).
The nat configuration command is the following:
natnat_numberconfignat-configuration
The following parameters can be configured:
ipip_address
Define an ip address to use for aliasing.
ifnic Use ip address of NIC for aliasing, dynamically changing it if
NIC's ip address changes.
log Enable logging on this nat instance.
deny_in
Deny any incoming connection from outside world.
same_ports
Try to leave the alias port numbers unchanged from the actual
local port numbers.
unreg_only
Traffic on the local network not originating from an unregistered
address spaces will be ignored.
reset Reset table of the packet aliasing engine on address change.
reverse
Reverse the way libalias handles aliasing.
proxy_only
Obey transparent proxy rules only, packet aliasing is not per-
formed.
skip_global
Skip instance in case of global state lookup (see below).
Some specials value can be supplied instead of nat_number:global Looks up translation state in all configured nat instances. If
an entry is found, packet is aliased according to that entry. If
no entry was found in any of the instances, packet is passed
unchanged, and no new entry will be created. See section
MULTIPLEINSTANCES in natd(8) for more information.
tablearg
Uses argument supplied in lookup table. See LOOKUPTABLES sec-
tion below for more information on lookup tables.
To let the packet continue after being (de)aliased, set the sysctl vari-
able net.inet.ip.fw.one_pass to 0. For more information about aliasing
modes, refer to libalias(3). See Section EXAMPLES for some examples
about nat usage.
REDIRECTANDLSNATSUPPORTINIPFW
Redirect and LSNAT support follow closely the syntax used in natd(8).
See Section EXAMPLES for some examples on how to do redirect and lsnat.
SCTPNATSUPPORT
SCTP nat can be configured in a similar manner to TCP through the ipfw
command line tool. The main difference is that sctpnat does not do port
translation. Since the local and global side ports will be the same,
there is no need to specify both. Ports are redirected as follows:
natnat_numberconfigifnicredirect_portsctpip_address[,addr_list]{[port | port-port][,ports]}
Most sctpnat configuration can be done in real-time through the
sysctl(8) interface. All may be changed dynamically, though the hash_ta-
ble size will only change for new nat instances. See SYSCTLVARIABLES
for more info.
IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATIONipfw supports in-kernel IPv6/IPv4 network address and protocol transla-
tion. Stateful NAT64 translation allows IPv6-only clients to contact
IPv4 servers using unicast TCP, UDP or ICMP protocols. One or more IPv4
addresses assigned to a stateful NAT64 translator are shared among
serveral IPv6-only clients. When stateful NAT64 is used in conjunction
with DNS64, no changes are usually required in the IPv6 client or the
IPv4 server. The kernel module ipfw_nat64 should be loaded or kernel
should have optionsIPFIREWALL_NAT64 to be able use stateful NAT64 trans-
lator.
Stateful NAT64 uses a bunch of memory for several types of objects. When
IPv6 client initiates connection, NAT64 translator creates a host entry
in the states table. Each host entry has a number of ports group entries
allocated on demand. Ports group entries contains connection state
entries. There are several options to control limits and lifetime for
these objects.
NAT64 translator follows RFC7915 when does ICMPv6/ICMP translation,
unsupported message types will be silently dropped. IPv6 needs several
ICMPv6 message types to be explicitly allowed for correct operation.
Make sure that ND6 neighbor solicitation (ICMPv6 type 135) and neighbor
advertisement (ICMPv6 type 136) messages will not be handled by transla-
tion rules.
After translation NAT64 translator sends packets through corresponding
netisr queue. Thus translator host should be configured as IPv4 and IPv6
router.
Currently both stateful and stateless NAT64 translators use Well-Known
IPv6 Prefix 64:ff9b::/96 to represent IPv4 addresses in the IPv6 address.
Thus DNS64 service and routing should be configured to use Well-Known
IPv6 Prefix.
The stateful NAT64 configuration command is the following:
nat64lsnnamecreatecreate-options
The following parameters can be configured:
prefix4ipv4_prefix/mask
The IPv4 prefix with mask defines the pool of IPv4 addresses used
as source address after translation. Stateful NAT64 module
translates IPv6 source address of client to one IPv4 address from
this pool. Note that incoming IPv4 packets that don't have cor-
responding state entry in the states table will be dropped by
translator. Make sure that translation rules handle packets,
destined to configured prefix.
max_portsnumber
Maximum number of ports reserved for upper level protocols to one
IPv6 client. All reserved ports are divided into chunks between
supported protocols. The number of connections from one IPv6
client is limited by this option. Note that closed TCP connec-
tions still remain in the list of connections until tcp_close_age
interval will not expire. Default value is 2048.
host_del_ageseconds
The number of seconds until the host entry for a IPv6 client will
be deleted and all its resources will be released due to inactiv-
ity. Default value is 3600.
pg_del_ageseconds
The number of seconds until a ports group with unused state
entries will be released. Default value is 900.
tcp_syn_ageseconds
The number of seconds while a state entry for TCP connection with
only SYN sent will be kept. If TCP connection establishing will
not be finished, state entry will be deleted. Default value is
10.
tcp_est_ageseconds
The number of seconds while a state entry for established TCP
connection will be kept. Default value is 7200.
tcp_close_ageseconds
The number of seconds while a state entry for closed TCP connec-
tion will be kept. Keeping state entries for closed connections
is needed, because IPv4 servers typically keep closed connections
in a TIME_WAIT state for a several minutes. Since translator's
IPv4 addresses are shared among all IPv6 clients, new connections
from the same addresses and ports may be rejected by server,
because these connections are still in a TIME_WAIT state. Keep-
ing them in translator's state table protects from such rejects.
Default value is 180.
udp_ageseconds
The number of seconds while translator keeps state entry in a
waiting for reply to the sent UDP datagram. Default value is
120.
icmp_ageseconds
The number of seconds while translator keeps state entry in a
waiting for reply to the sent ICMP message. Default value is 60.
log Turn on logging of all handled packets via BPF through ipfwlog0
interface. ipfwlog0 is a pseudo interface and can be created
after a boot manually with ifconfig command. Note that it has
different purpose than ipfw0 interface. Translators sends to BPF
an additional information with each packet. With tcpdump you are
able to see each handled packet before and after translation.
-log Turn off logging of all handled packets via BPF.
To inspect a states table of stateful NAT64 the following command can be
used:
nat64lsnnameshowstates
Stateless NAT64 translator doesn't use a states table for translation and
converts IPv4 addresses to IPv6 and vice versa solely based on the map-
pings taken from configured lookup tables. Since a states table doesn't
used by stateless translator, it can be configured to pass IPv4 clients
to IPv6-only servers.
The stateless NAT64 configuration command is the following:
nat64stlnamecreatecreate-options
The following parameters can be configured:
table4table46
The lookup table table46 contains mapping how IPv4 addresses
should be translated to IPv6 addresses.
table6table64
The lookup table table64 contains mapping how IPv6 addresses
should be translated to IPv4 addresses.
log Turn on logging of all handled packets via BPF through ipfwlog0
interface.
-log Turn off logging of all handled packets via BPF.
Note that the behavior of stateless translator with respect to not
matched packets differs from stateful translator. If corresponding
addresses was not found in the lookup tables, the packet will not be
dropped and the search continues.
IPv6-to-IPv6 NETWORK PREFIX TRANSLATION (NPTv6)ipfw supports in-kernel IPv6-to-IPv6 network prefix translation as
described in RFC6296. The kernel module ipfw_nptv6 should be loaded or
kernel should has optionsIPFIREWALL_NPTV6 to be able use NPTv6 transla-
tor.
The NPTv6 configuration command is the following:
nptv6namecreatecreate-options
The following parameters can be configured:
int_prefixipv6_prefix
IPv6 prefix used in internal network. NPTv6 module translates
source address when it matches this prefix.
ext_prefixipv6_prefix
IPv6 prefix used in external network. NPTv6 module translates
destination address when it matches this prefix.
prefixlenlength
The length of specified IPv6 prefixes. It must be in range from 8
to 64.
Note that the prefix translation rules are silently ignored when IPv6
packet forwarding is disabled. To enable the packet forwarding, set the
sysctl variable net.inet6.ip6.forwarding to 1.
To let the packet continue after being translated, set the sysctl vari-
able net.inet.ip.fw.one_pass to 0.
LOADER TUNABLES
Tunables can be set in loader(8) prompt, loader.conf(5) or kenv(1) before
ipfw module gets loaded.
net.inet.ip.fw.default_to_accept: 0
Defines ipfw last rule behavior. This value overrides optionsIPFW_DEFAULT_TO_(ACCEPT|DENY) from kernel configuration file.
net.inet.ip.fw.tables_max: 128
Defines number of tables available in ipfw. Number cannot exceed
65534.
SYSCTL VARIABLES
A set of sysctl(8) variables controls the behaviour of the firewall and
associated modules (dummynet, bridge, sctpnat). These are shown below
together with their default value (but always check with the sysctl(8)
command what value is actually in use) and meaning:
net.inet.ip.alias.sctp.accept_global_ootb_addip: 0
Defines how the nat responds to receipt of global OOTB ASCONF-
AddIP:
0 No response (unless a partially matching association
exists - ports and vtags match but global address does
not)
1nat will accept and process all OOTB global AddIP mes-
sages.
Option 1 should never be selected as this forms a security risk.
An attacker can establish multiple fake associations by sending
AddIP messages.
net.inet.ip.alias.sctp.chunk_proc_limit: 5
Defines the maximum number of chunks in an SCTP packet that will
be parsed for a packet that matches an existing association.
This value is enforced to be greater or equal than
net.inet.ip.alias.sctp.initialising_chunk_proc_limit. A high
value is a DoS risk yet setting too low a value may result in
important control chunks in the packet not being located and
parsed.
net.inet.ip.alias.sctp.error_on_ootb: 1
Defines when the nat responds to any Out-of-the-Blue (OOTB) pack-
ets with ErrorM packets. An OOTB packet is a packet that arrives
with no existing association registered in the nat and is not an
INIT or ASCONF-AddIP packet:
0 ErrorM is never sent in response to OOTB packets.
1 ErrorM is only sent to OOTB packets received on the local
side.
2 ErrorM is sent to the local side and on the global side
ONLY if there is a partial match (ports and vtags match
but the source global IP does not). This value is only
useful if the nat is tracking global IP addresses.
3 ErrorM is sent in response to all OOTB packets on both
the local and global side (DoS risk).
At the moment the default is 0, since the ErrorM packet is not
yet supported by most SCTP stacks. When it is supported, and if
not tracking global addresses, we recommend setting this value to
1 to allow multi-homed local hosts to function with the nat. To
track global addresses, we recommend setting this value to 2 to
allow global hosts to be informed when they need to (re)send an
ASCONF-AddIP. Value 3 should never be chosen (except for debug-
ging) as the nat will respond to all OOTB global packets (a DoS
risk).
net.inet.ip.alias.sctp.hashtable_size: 2003
Size of hash tables used for nat lookups (100 < prime_number >
1000001). This value sets the hashtable size for any future
created nat instance and therefore must be set prior to creating
a nat instance. The table sizes may be changed to suit specific
needs. If there will be few concurrent associations, and memory
is scarce, you may make these smaller. If there will be many
thousands (or millions) of concurrent associations, you should
make these larger. A prime number is best for the table size.
The sysctl update function will adjust your input value to the
next highest prime number.
net.inet.ip.alias.sctp.holddown_time: 0
Hold association in table for this many seconds after receiving a
SHUTDOWN-COMPLETE. This allows endpoints to correct shutdown
gracefully if a shutdown_complete is lost and retransmissions are
required.
net.inet.ip.alias.sctp.init_timer: 15
Timeout value while waiting for (INIT-ACK|AddIP-ACK). This value
cannot be 0.
net.inet.ip.alias.sctp.initialising_chunk_proc_limit: 2
Defines the maximum number of chunks in an SCTP packet that will
be parsed when no existing association exists that matches that
packet. Ideally this packet will only be an INIT or ASCONF-AddIP
packet. A higher value may become a DoS risk as malformed pack-
ets can consume processing resources.
net.inet.ip.alias.sctp.param_proc_limit: 25
Defines the maximum number of parameters within a chunk that will
be parsed in a packet. As for other similar sysctl variables,
larger values pose a DoS risk.
net.inet.ip.alias.sctp.log_level: 0
Level of detail in the system log messages (0 - minimal, 1 -
event, 2 - info, 3 - detail, 4 - debug, 5 - max debug). May be a
good option in high loss environments.
net.inet.ip.alias.sctp.shutdown_time: 15
Timeout value while waiting for SHUTDOWN-COMPLETE. This value
cannot be 0.
net.inet.ip.alias.sctp.track_global_addresses: 0
Enables/disables global IP address tracking within the nat and
places an upper limit on the number of addresses tracked for each
association:
0 Global tracking is disabled
>1 Enables tracking, the maximum number of addresses tracked
for each association is limited to this value
This variable is fully dynamic, the new value will be adopted for
all newly arriving associations, existing associations are
treated as they were previously. Global tracking will decrease
the number of collisions within the nat at a cost of increased
processing load, memory usage, complexity, and possible nat state
problems in complex networks with multiple nats. We recommend
not tracking global IP addresses, this will still result in a
fully functional nat.
net.inet.ip.alias.sctp.up_timer: 300
Timeout value to keep an association up with no traffic. This
value cannot be 0.
net.inet.ip.dummynet.expire: 1
Lazily delete dynamic pipes/queue once they have no pending traf-
fic. You can disable this by setting the variable to 0, in which
case the pipes/queues will only be deleted when the threshold is
reached.
net.inet.ip.dummynet.hash_size: 64
Default size of the hash table used for dynamic pipes/queues.
This value is used when no buckets option is specified when con-
figuring a pipe/queue.
net.inet.ip.dummynet.io_fast: 0
If set to a non-zero value, the ``fast'' mode of dummynet opera-
tion (see above) is enabled.
net.inet.ip.dummynet.io_pkt
Number of packets passed to dummynet.
net.inet.ip.dummynet.io_pkt_drop
Number of packets dropped by dummynet.
net.inet.ip.dummynet.io_pkt_fast
Number of packets bypassed by the dummynet scheduler.
net.inet.ip.dummynet.max_chain_len: 16
Target value for the maximum number of pipes/queues in a hash
bucket. The product max_chain_len*hash_size is used to determine
the threshold over which empty pipes/queues will be expired even
when net.inet.ip.dummynet.expire=0.
net.inet.ip.dummynet.red_lookup_depth: 256
net.inet.ip.dummynet.red_avg_pkt_size: 512
net.inet.ip.dummynet.red_max_pkt_size: 1500
Parameters used in the computations of the drop probability for
the RED algorithm.
net.inet.ip.dummynet.pipe_byte_limit: 1048576
net.inet.ip.dummynet.pipe_slot_limit: 100
The maximum queue size that can be specified in bytes or packets.
These limits prevent accidental exhaustion of resources such as
mbufs. If you raise these limits, you should make sure the sys-
tem is configured so that sufficient resources are available.
net.inet.ip.fw.autoinc_step: 100
Delta between rule numbers when auto-generating them. The value
must be in the range 1..1000.
net.inet.ip.fw.curr_dyn_buckets: net.inet.ip.fw.dyn_buckets
The current number of buckets in the hash table for dynamic rules
(readonly).
net.inet.ip.fw.debug: 1
Controls debugging messages produced by ipfw.
net.inet.ip.fw.default_rule: 65535
The default rule number (read-only). By the design of ipfw, the
default rule is the last one, so its number can also serve as the
highest number allowed for a rule.
net.inet.ip.fw.dyn_buckets: 256
The number of buckets in the hash table for dynamic rules. Must
be a power of 2, up to 65536. It only takes effect when all
dynamic rules have expired, so you are advised to use a flush
command to make sure that the hash table is resized.
net.inet.ip.fw.dyn_count: 3
Current number of dynamic rules (read-only).
net.inet.ip.fw.dyn_keepalive: 1
Enables generation of keepalive packets for keep-state rules on
TCP sessions. A keepalive is generated to both sides of the con-
nection every 5 seconds for the last 20 seconds of the lifetime
of the rule.
net.inet.ip.fw.dyn_max: 8192
Maximum number of dynamic rules. When you hit this limit, no
more dynamic rules can be installed until old ones expire.
net.inet.ip.fw.dyn_ack_lifetime: 300
net.inet.ip.fw.dyn_syn_lifetime: 20
net.inet.ip.fw.dyn_fin_lifetime: 1
net.inet.ip.fw.dyn_rst_lifetime: 1
net.inet.ip.fw.dyn_udp_lifetime: 5
net.inet.ip.fw.dyn_short_lifetime: 30
These variables control the lifetime, in seconds, of dynamic
rules. Upon the initial SYN exchange the lifetime is kept short,
then increased after both SYN have been seen, then decreased
again during the final FIN exchange or when a RST is received.
Both dyn_fin_lifetime and dyn_rst_lifetime must be strictly lower
than 5 seconds, the period of repetition of keepalives. The
firewall enforces that.
net.inet.ip.fw.dyn_keep_states: 0
Keep dynamic states on rule/set deletion. States are relinked to
default rule (65535). This can be handly for ruleset reload.
Turned off by default.
net.inet.ip.fw.enable: 1
Enables the firewall. Setting this variable to 0 lets you run
your machine without firewall even if compiled in.
net.inet6.ip6.fw.enable: 1
provides the same functionality as above for the IPv6 case.
net.inet.ip.fw.one_pass: 1
When set, the packet exiting from the dummynet pipe or from
ng_ipfw(4) node is not passed though the firewall again. Other-
wise, after an action, the packet is reinjected into the firewall
at the next rule.
net.inet.ip.fw.tables_max: 128
Maximum number of tables.
net.inet.ip.fw.verbose: 1
Enables verbose messages.
net.inet.ip.fw.verbose_limit: 0
Limits the number of messages produced by a verbose firewall.
net.inet6.ip6.fw.deny_unknown_exthdrs: 1
If enabled packets with unknown IPv6 Extension Headers will be
denied.
net.link.ether.ipfw: 0
Controls whether layer-2 packets are passed to ipfw. Default is
no.
net.link.bridge.ipfw: 0
Controls whether bridged packets are passed to ipfw. Default is
no.
INTERNAL DIAGNOSTICS
There are some commands that may be useful to understand current state of
certain subsystems inside kernel module. These commands provide debug-
ging output which may change without notice.
Currently the following commands are available as internal sub-options:
iflist Lists all interface which are currently tracked by ipfw with
their in-kernel status.
talist List all table lookup algorithms currently available.
EXAMPLES
There are far too many possible uses of ipfw so this Section will only
give a small set of examples.
BASICPACKETFILTERING
This command adds an entry which denies all tcp packets from
cracker.evil.org to the telnet port of wolf.tambov.su from being for-
warded by the host:
ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet
This one disallows any connection from the entire cracker's network to my
host:
ipfw add deny ip from 123.45.67.0/24 to my.host.org
A first and efficient way to limit access (not using dynamic rules) is
the use of the following rules:
ipfw add allow tcp from any to any established
ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup
ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup
...
ipfw add deny tcp from any to any
The first rule will be a quick match for normal TCP packets, but it will
not match the initial SYN packet, which will be matched by the setup
rules only for selected source/destination pairs. All other SYN packets
will be rejected by the final deny rule.
If you administer one or more subnets, you can take advantage of the
address sets and or-blocks and write extremely compact rulesets which
selectively enable services to blocks of clients, as below:
goodguys="{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }"
badguys="10.1.2.0/24{8,38,60}"
ipfw add allow ip from ${goodguys} to any
ipfw add deny ip from ${badguys} to any
... normal policies ...
The verrevpath option could be used to do automated anti-spoofing by
adding the following to the top of a ruleset:
ipfw add deny ip from any to any not verrevpath in
This rule drops all incoming packets that appear to be coming to the sys-
tem on the wrong interface. For example, a packet with a source address
belonging to a host on a protected internal network would be dropped if
it tried to enter the system from an external interface.
The antispoof option could be used to do similar but more restricted
anti-spoofing by adding the following to the top of a ruleset:
ipfw add deny ip from any to any not antispoof in
This rule drops all incoming packets that appear to be coming from
another directly connected system but on the wrong interface. For exam-
ple, a packet with a source address of 192.168.0.0/24, configured on
fxp0, but coming in on fxp1 would be dropped.
The setdscp option could be used to (re)mark user traffic, by adding the
following to the appropriate place in ruleset:
ipfw add setdscp be ip from any to any dscp af11,af21
DYNAMICRULES
In order to protect a site from flood attacks involving fake TCP packets,
it is safer to use dynamic rules:
ipfw add check-state
ipfw add deny tcp from any to any established
ipfw add allow tcp from my-net to any setup keep-state
This will let the firewall install dynamic rules only for those connec-
tion which start with a regular SYN packet coming from the inside of our
network. Dynamic rules are checked when encountering the first occur-
rence of a check-state, keep-state or limit rule. A check-state rule
should usually be placed near the beginning of the ruleset to minimize
the amount of work scanning the ruleset. Your mileage may vary.
To limit the number of connections a user can open you can use the fol-
lowing type of rules:
ipfw add allow tcp from my-net/24 to any setup limit src-addr 10
ipfw add allow tcp from any to me setup limit src-addr 4
The former (assuming it runs on a gateway) will allow each host on a /24
network to open at most 10 TCP connections. The latter can be placed on
a server to make sure that a single client does not use more than 4
simultaneous connections.
BEWARE: stateful rules can be subject to denial-of-service attacks by a
SYN-flood which opens a huge number of dynamic rules. The effects of
such attacks can be partially limited by acting on a set of sysctl(8)
variables which control the operation of the firewall.
Here is a good usage of the list command to see accounting records and
timestamp information:
ipfw -at list
or in short form without timestamps:
ipfw -a list
which is equivalent to:
ipfw show
Next rule diverts all incoming packets from 192.168.2.0/24 to divert port
5000:
ipfw divert 5000 ip from 192.168.2.0/24 to any in
TRAFFICSHAPING
The following rules show some of the applications of ipfw and dummynet
for simulations and the like.
This rule drops random incoming packets with a probability of 5%:
ipfw add prob 0.05 deny ip from any to any in
A similar effect can be achieved making use of dummynet pipes:
ipfw add pipe 10 ip from any to any
ipfw pipe 10 config plr 0.05
We can use pipes to artificially limit bandwidth, e.g. on a machine act-
ing as a router, if we want to limit traffic from local clients on
192.168.2.0/24 we do:
ipfw add pipe 1 ip from 192.168.2.0/24 to any out
ipfw pipe 1 config bw 300Kbit/s queue 50KBytes
note that we use the out modifier so that the rule is not used twice.
Remember in fact that ipfw rules are checked both on incoming and outgo-
ing packets.
Should we want to simulate a bidirectional link with bandwidth limita-
tions, the correct way is the following:
ipfw add pipe 1 ip from any to any out
ipfw add pipe 2 ip from any to any in
ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes
ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes
The above can be very useful, e.g. if you want to see how your fancy Web
page will look for a residential user who is connected only through a
slow link. You should not use only one pipe for both directions, unless
you want to simulate a half-duplex medium (e.g. AppleTalk, Ethernet,
IRDA). It is not necessary that both pipes have the same configuration,
so we can also simulate asymmetric links.
Should we want to verify network performance with the RED queue manage-
ment algorithm:
ipfw add pipe 1 ip from any to any
ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1
Another typical application of the traffic shaper is to introduce some
delay in the communication. This can significantly affect applications
which do a lot of Remote Procedure Calls, and where the round-trip-time
of the connection often becomes a limiting factor much more than band-
width:
ipfw add pipe 1 ip from any to any out
ipfw add pipe 2 ip from any to any in
ipfw pipe 1 config delay 250ms bw 1Mbit/s
ipfw pipe 2 config delay 250ms bw 1Mbit/s
Per-flow queueing can be useful for a variety of purposes. A very simple
one is counting traffic:
ipfw add pipe 1 tcp from any to any
ipfw add pipe 1 udp from any to any
ipfw add pipe 1 ip from any to any
ipfw pipe 1 config mask all
The above set of rules will create queues (and collect statistics) for
all traffic. Because the pipes have no limitations, the only effect is
collecting statistics. Note that we need 3 rules, not just the last one,
because when ipfw tries to match IP packets it will not consider ports,
so we would not see connections on separate ports as different ones.
A more sophisticated example is limiting the outbound traffic on a net
with per-host limits, rather than per-network limits:
ipfw add pipe 1 ip from 192.168.2.0/24 to any out
ipfw add pipe 2 ip from any to 192.168.2.0/24 in
ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue
20Kbytes
ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue
20Kbytes
LOOKUPTABLES
In the following example, we need to create several traffic bandwidth
classes and we need different hosts/networks to fall into different
classes. We create one pipe for each class and configure them accord-
ingly. Then we create a single table and fill it with IP subnets and
addresses. For each subnet/host we set the argument equal to the number
of the pipe that it should use. Then we classify traffic using a single
rule:
ipfw pipe 1 config bw 1000Kbyte/s
ipfw pipe 4 config bw 4000Kbyte/s
...
ipfw table T1 create type addr
ipfw table T1 add 192.168.2.0/24 1
ipfw table T1 add 192.168.0.0/27 4
ipfw table T1 add 192.168.0.2 1
...
ipfw add pipe tablearg ip from 'table(T1)' to any
Using the fwd action, the table entries may include hostnames and IP
addresses.
ipfw table T2 create type addr ftype ip
ipfw table T2 add 192.168.2.0/24 10.23.2.1
ipfw table T21 add 192.168.0.0/27 router1.dmz
...
ipfw add 100 fwd tablearg ip from any to table(1)
In the following example per-interface firewall is created:
ipfw table IN create type iface valtype skipto,fib
ipfw table IN add vlan20 12000,12
ipfw table IN add vlan30 13000,13
ipfw table OUT create type iface valtype skipto
ipfw table OUT add vlan20 22000
ipfw table OUT add vlan30 23000
..
ipfw add 100 ipfw setfib tablearg ip from any to any recv
'table(IN)' in
ipfw add 200 ipfw skipto tablearg ip from any to any recv
'table(IN)' in
ipfw add 300 ipfw skipto tablearg ip from any to any xmit
'table(OUT)' out
The following example illustrate usage of flow tables:
ipfw table fl create type flow:flow:src-ip,proto,dst-ip,dst-port
ipfw table fl add 2a02:6b8:77::88,tcp,2a02:6b8:77::99,80 11
ipfw table fl add 10.0.0.1,udp,10.0.0.2,53 12
..
ipfw add 100 allow ip from any to any flow 'table(fl,11)' recv ix0
SETSOFRULES
To add a set of rules atomically, e.g. set 18:
ipfw set disable 18
ipfw add NN set 18 ... # repeat as needed
ipfw set enable 18
To delete a set of rules atomically the command is simply:
ipfw delete set 18
To test a ruleset and disable it and regain control if something goes
wrong:
ipfw set disable 18
ipfw add NN set 18 ... # repeat as needed
ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18
Here if everything goes well, you press control-C before the "sleep" ter-
minates, and your ruleset will be left active. Otherwise, e.g. if you
cannot access your box, the ruleset will be disabled after the sleep ter-
minates thus restoring the previous situation.
To show rules of the specific set:
ipfw set 18 show
To show rules of the disabled set:
ipfw -S set 18 show
To clear a specific rule counters of the specific set:
ipfw set 18 zero NN
To delete a specific rule of the specific set:
ipfw set 18 delete NN
NAT,REDIRECTANDLSNAT
First redirect all the traffic to nat instance 123:
ipfw add nat 123 all from any to any
Then to configure nat instance 123 to alias all the outgoing traffic with
ip 192.168.0.123, blocking all incoming connections, trying to keep same
ports on both sides, clearing aliasing table on address change and keep-
ing a log of traffic/link statistics:
ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports
Or to change address of instance 123, aliasing table will be cleared (see
reset option):
ipfw nat 123 config ip 10.0.0.1
To see configuration of nat instance 123:
ipfw nat 123 show config
To show logs of all the instances in range 111-999:
ipfw nat 111-999 show
To see configurations of all instances:
ipfw nat show config
Or a redirect rule with mixed modes could looks like:
ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66
redirect_port tcp 192.168.0.1:80 500
redirect_proto udp 192.168.1.43 192.168.1.1
redirect_addr 192.168.0.10,192.168.0.11
10.0.0.100 # LSNAT
redirect_port tcp 192.168.0.1:80,192.168.0.10:22
500 # LSNAT
or it could be split in:
ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66
ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500
ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1
ipfw nat 4 config redirect_addr
192.168.0.10,192.168.0.11,192.168.0.12
10.0.0.100
ipfw nat 5 config redirect_port tcp
192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500
SEE ALSOcpp(1), m4(1), altq(4), divert(4), dummynet(4), if_bridge(4), ip(4),
ipfirewall(4), ng_ipfw(4), protocols(5), services(5), init(8),
kldload(8), reboot(8), sysctl(8), syslogd(8)HISTORY
The ipfw utility first appeared in FreeBSD 2.0. dummynet was introduced
in FreeBSD 2.2.8. Stateful extensions were introduced in FreeBSD 4.0.
ipfw2 was introduced in Summer 2002.
AUTHORS
Ugen J. S. Antsilevich,
Poul-Henning Kamp,
Alex Nash,
Archie Cobbs,
Luigi Rizzo.
API based upon code written by Daniel Boulet for BSDI.
Dummynet has been introduced by Luigi Rizzo in 1997-1998.
Some early work (1999-2000) on the dummynet traffic shaper supported by
Akamba Corp.
The ipfw core (ipfw2) has been completely redesigned and reimplemented by
Luigi Rizzo in summer 2002. Further actions and options have been added
by various developer over the years.
In-kernel NAT support written by Paolo Pisati <piso@FreeBSD.org> as part
of a Summer of Code 2005 project.
SCTP nat support has been developed by The Centre for Advanced Internet
Architectures (CAIA) <http://www.caia.swin.edu.au>. The primary develop-
ers and maintainers are David Hayes and Jason But. For further informa-
tion visit: <http://www.caia.swin.edu.au/urp/SONATA>
Delay profiles have been developed by Alessandro Cerri and Luigi Rizzo,
supported by the European Commission within Projects Onelab and Onelab2.
BUGS
The syntax has grown over the years and sometimes it might be confusing.
Unfortunately, backward compatibility prevents cleaning up mistakes made
in the definition of the syntax.
!!!WARNING!!!
Misconfiguring the firewall can put your computer in an unusable state,
possibly shutting down network services and requiring console access to
regain control of it.
Incoming packet fragments diverted by divert are reassembled before
delivery to the socket. The action used on those packet is the one from
the rule which matches the first fragment of the packet.
Packets diverted to userland, and then reinserted by a userland process
may lose various packet attributes. The packet source interface name
will be preserved if it is shorter than 8 bytes and the userland process
saves and reuses the sockaddr_in (as does natd(8)); otherwise, it may be
lost. If a packet is reinserted in this manner, later rules may be
incorrectly applied, making the order of divert rules in the rule
sequence very important.
Dummynet drops all packets with IPv6 link-local addresses.
Rules using uid or gid may not behave as expected. In particular, incom-
ing SYN packets may have no uid or gid associated with them since they do
not yet belong to a TCP connection, and the uid/gid associated with a
packet may not be as expected if the associated process calls setuid(2)
or similar system calls.
Rule syntax is subject to the command line environment and some patterns
may need to be escaped with the backslash character or quoted appropri-
ately.
Due to the architecture of libalias(3), ipfw nat is not compatible with
the TCP segmentation offloading (TSO). Thus, to reliably nat your net-
work traffic, please disable TSO on your NICs using ifconfig(8).
ICMP error messages are not implicitly matched by dynamic rules for the
respective conversations. To avoid failures of network error detection
and path MTU discovery, ICMP error messages may need to be allowed
explicitly through static rules.
Rules using call and return actions may lead to confusing behaviour if
ruleset has mistakes, and/or interaction with other subsystems (netgraph,
dummynet, etc.) is used. One possible case for this is packet leaving
ipfw in subroutine on the input pass, while later on output encountering
unpaired return first. As the call stack is kept intact after input
pass, packet will suddenly return to the rule number used on input pass,
not on output one. Order of processing should be checked carefully to
avoid such mistakes.
FreeBSD 11.2 March 19, 2018 FreeBSD 11.2